As a method of thinning a semiconductor wafer, there has been known a method called the TAIKO process which leaves an ring of a few millimeters in width on the outer edge of the wafer and grinds only the inner area of the back surface of the wafer. According to the above method, the semiconductor wafer has the outer peripheral portion that is not ground to remain with its original thickness, so that mechanical strength of the wafer is maintained, and it is possible to suppress cracking or warpage of the semiconductor wafer at the time of the semiconductor wafer being processed or transferred thereafter.
In the TAIKO process, when grinding the inner area, normally, for increasing an index, rough grinding is performed with a grindstone with a coarse grain size, and next finish grinding is performed with a grindstone with a fine grain size. In the above case, in the finish grinding, an inner region is ground rather than a region to be ground in the rough grinding, so that a rough ground surface remains around the outer periphery of the finish ground region. As a result, the semiconductor wafer has a problem that cracking easily occurs starting from the above rough ground surface. Such ease of occurrence of cracking is significant as the thickness of the semiconductor wafer becomes thinner.